In order to change the resolution in KDE, there is the very simple sequence: Ctl+Alt+"-" and Ctl+Alt+"+", which changes the resolution down and up through the next possible lower or higher settings. * Use the "+" and "-" keys on the numerical pad.
If that does not help, the necessary settings must be input in the /etc/X11/XF86Config-4 file. Never put a setting higher than your screen can deal with, otherwise the Desktop does not fit on the screen. (Note: One can force this effect; called Virtual Desktop which offers more pixels than the screen can display. So one example is 1280x1024 pixel big, and one looks at it through the tube (of the physical monitor) as by a looking port, and thus sees a portion in each case (e.g., 1024x768). One shifts this cutout on the full 1280x1024 points, by going with the mouse to the edge of screen. It is a funny effect, but I doubt whether it is really very practical.
Input in the file /etc/X11/XF86Config-4, the appropriate line for your maximum resolution (without scrolling): Look for the line:
Then put in the line the correct depth of colour (the ones used are indicated as DefaultColorDepth?
=xy before the first Sub Section "Display"). Your values e.g.:
Modes "1024x768" "800x600" "640x480"
# If you wants a virtual Desktop, remove the number sign in the following line
# Virtual 1280 1024
End Sub Section
Here the maximum resolution is 1024x768.
*Note: The resolutions, which can be selected with Ctl+Alt+ "+/-", are those, which were indicated as Modes
(as mentioned above)!